Determination And Application Of Trace Elements In Sediments And Crude Oil By Inductively Coupled Plasma Mass Spectrometry

Trace elements within sediments and crude oil have great geochemical and environmental significance（e.g.genetic analysis,source identification,ecological quality evaluation）though their contents are typically low.Besides,trace elements within crude oil significantly impact the oil refining process and quality of the products,the catalyst activity in the petroleum catalytic cracking process could also be affected.Hence,it is crucial to establish an accurate analytical method so as to determine trace elements within those samples rapidly.Inductively coupled plasma mass spectrometer（ICP-MS）has been widely applied in trace elements determination and analysis for various fields in terms of its significant performance of low detection limit,high selectivity,great reproducibility,wide linear ranges,time-saving,and capacity of multiple element analysis.Sedimentary rocks such as shale,sandstone,and mudstone are types of rock that are formed by sediments through deposition and subsequent cementation processes.There exits various methods to pre-treat those samples.However,by virtue of high abundance organic compounds,loss of sample components could be easily found without the proper care,and mass spectrum interference and carbon deposition on the surface of cone could be introduced by uncompleted digestion.The study compared the performance of sediment sample digestion after microwave digestion and pressurized acid digestion,and discussed affections of parameters（e.g.amounts of reagents,digestion systems,digestion time）on the performance of crude oil sample digestion.Subsequently pressurized acid digestion was regarded as the pre-treatment method.For 150 mg crude oil samples,the HNO₃-H₂O₂digestion system with 6 mL concentrated nitric acid and 2 mL hydrogen peroxide was selected;the samples digested under 100℃for 4 hours,subsequently under 145℃for 20 hours.In order to enhance the analytical accuracy,the study determined trace elements in comparison with the standard curve method and standard addition method.Results present that 85%¹19%recoveries could be obtained in association with the standard addition method in analyzing certificated reference materials of shale,better than the standard curve method with 68%¹60%recoveries.Besides,calibration curves for shale with standard solutions were applied to analyze certificated reference materials of argillaceous limestone so as to improve the efficiency.Recoveries of analysed elements were between 85%¹23%and relative standard deviation was less than 10%.The results indicate that calibration curves for one sample with standard addition method could be effectively applied in handling samples with similar matrix.In consideration of analyzing certificated reference materials of shale,sediment samples,and crude oil samples by the present method,results show that the correlation coefficients of fitting linear equation were all greater than 0.991,and relative standard deviation was less than 10%.Also,calibration curves obtained above had been applied to analyze sediment samples.Moreover,crude oil samples of ym-4 and P-13 were analyzed through same process,and the correlation coefficients of fitting linear equation were all greater than 0.99.Calibration curves for P-13 was induced to analyze crude oil samples,and great analytical accuracy was obtained with relative standard deviation less than 11%.